A STOVL aircraft is a fixed wing aircraft that is able to take off from a short runway or even vertically in some circumstances, and land vertically. To achieve vertical lift, the aircraft uses a lift fan that to provide vertical thrust. The use of a short runway allows the aircraft to carry a larger payload than a purely VTOL (vertical takeoff and landing) aircraft, although the two types are closely related, particularly when it comes to achieving vertical lift. For the purposes of this application, STOVL should be interpreted as also including VTOL.
Since STOVL aircraft are fixed wing, they have the need to provide vertical lift during takeoff and landing, but forward propulsion during flight. Prior art aircraft provide vertical lift in a variety of ways. One known method is to redirect some portion of the airflow generated by the main turbine used during forward flight in a downward direction using vectoring nozzles. This method is used, for example, by Hawker Siddeley Harrier aircraft.
Another prior art aircraft is the F-35 Lightning which uses a separate lift fan that is connected to the main engine by a drive shaft. This type of system is shown, for example, in U.S. Pat. No. 8,910,464. However, this type of system creates a large load on the main engine, leading to breakage and other problems associated with extra torque on the engine.
Thus, a need exists for a lift fan in a STOVL aircraft that eliminates the drag and torque on the main engine and reduces fuel cost and engine wear.